CHAPTER II. VARIATION UNDER NATURE.

6. MANY OF THE SPECIES INCLUDED WITHIN THE LARGER GENERA RESEMBLE VARIETIES IN BEING VERY CLOSELY, BUT UNEQUALLY, RELATED TO EACH OTHER, AND IN HAVING RESTRICTED RANGES. (continued)

There is one other point which is worth notice. Varieties generally have
much restricted ranges. This statement is indeed scarcely more than a
truism, for if a variety were found to have a wider range than that of its
supposed parent-species, their denominations would be reversed. But there
is reason to believe that the species which are very closely allied to
other species, and in so far resemble varieties, often have much restricted
ranges. For instance, Mr. H.C. Watson has marked for me in the well-sifted
London catalogue of Plants (4th edition) sixty-three plants which are
therein ranked as species, but which he considers as so closely allied to
other species as to be of doubtful value: these sixty-three reputed
species range on an average over 6.9 of the provinces into which Mr. Watson
has divided Great Britain. Now, in this same catalogue, fifty-three
acknowledged varieties are recorded, and these range over 7.7 provinces;
whereas, the species to which these varieties belong range over 14.3
provinces. So that the acknowledged varieties have very nearly the same
restricted average range, as have the closely allied forms, marked for me
by Mr. Watson as doubtful species, but which are almost universally ranked
by British botanists as good and true species.